* Yanukovich office says deal to be signed Friday
* EU ministers hold "difficult night" of talks
* Death toll in two days violence reaches 75
* Ratings agency S&P downgrades Ukraine again (Adds Fabius)
By Pavel Polityuk and Natalia Zinets
KIEV, Feb 21 (Reuters) - Ukrainian President Viktor Yanukovich said on Friday a deal to resolve his country's political crisis had been reached with pro-European opposition leaders after the worst violence since Soviet times, but France urged caution.
After all-night negotiations mediated by visiting European Union foreign ministers, the presidential press service said an agreement would be signed at noon (1000 GMT) but gave no details.
French foreign minister Laurent Fabius, who is involved in the mediation attempt, said the opposition needed to consult.
"The opposition wants to consult with some of its members, which is entirely understandable," Fabius said in a live interview on Europe 1 radio. "In this sort of situation, as long as things haven't really been wrapped up, it's important to remain very cautious."
Anti-government protesters encamped in Kiev's central Independence Square were deeply sceptical of any announcement from the Russian-backed president.
After 48 hours in which the fate of Ukraine was fought out in the square, with at least 75 people killed, the Russian-backed Yanukovich was rapidly losing support and faced the risk of civil war or even a break-up of the sprawling country of 46 million.
As the president's position weakened rapidly, the deputy chief of the armed forces resigned and opposition deputies in parliament voted to overturn severe anti-terrorist laws enacted by Yanukovich's government this month and ordered security forces back to barracks.
In another sign of the severity of the crisis, ratings agency Standard & Poor's cut Ukraine's credit rating for the second time in three weeks on Friday, citing the increased risk of default.
Polish Foreign Minister Radoslaw Sikorski, in Kiev with his German and French counterparts, tweeted a few minutes before the presidential announcement that the talks had been suspended.
"After negotiations through the night, talks ended at 7:20 (0520 GMT)," Sikorski said via his Twitter account.
The ministers were trying to broker a deal on a temporary government and early elections this year after gun battles between police and protesters caused the worst bloodshed since Ukraine emerged from the collapsing Soviet Union 22 years ago.
Three hours of fierce fighting on Thursday in which protesters recaptured the square, known as Maidan or "Euro-Maidan", left the bodies of over 20 civilians strewn on the ground, a short walk from Yanukovich's office.
France's foreign minister left for Beijing during the night after saying there was still no agreement over a proposed road map to ease the crisis, which erupted in November after Yanukovich abandoned a proposed trade deal with the European Union and turned instead towards Moscow.
"There is no agreement for now, the negotiations are very difficult and we are working to reach a peaceful solution," Laurent Fabius told reporters.
Sikorski and German Foreign Minister Frank-Walter Steinmeier stayed on in Kiev on Friday to try to secure a deal.
"We have to find every way to see how we can put a new government in place, think about elections and see how we can end the violence, but at this moment there is no solution," Fabius said.
Earlier in the day, riot police were captured on video shooting from a rooftop at demonstrators in the central plaza. Protesters hurled petrol bombs and paving stones to drive the security forces off a corner of the square the police had captured in battles that began two days earlier.
The health ministry said 75 people had been killed since Tuesday afternoon, which meant at least 47 died in Thursday's clashes. That was by far the worst violence since Ukraine's independence.
The trio of visiting foreign ministers met Yanukovich and the opposition after EU colleagues in Brussels imposed targeted sanctions on Ukraine and threatened more if the authorities failed to restore calm.
In further diplomatic efforts, U.S. President Barack Obama spoke to German Chancellor Angela Merkel who in turn discussed Ukraine with Russian President Vladimir Putin.
Putin "stressed the critical importance of an immediate end to bloodshed, the need to take urgent measures to stabilise the situation and suppress extremist and terrorist attacks" the Kremlin said - sharing Yanukovich's view that he faces a coup.
The White House said Obama and Merkel agreed it was "critical" U.S. and EU leaders "stay in close touch in the days ahead on steps we can take to support an end to the violence and a political solution that is in the best interests of the Ukrainian people". Earlier this month, bugged and leaked diplomatic phone calls exposed EU-U.S. disagreement on Ukraine.
The EU plan "offers a chance to bring an end to violence," Polish Prime Minister Donald Tusk said in Warsaw, adding that Yanukovich was willing to hold rapid elections to parliament and the presidency - the latter something Yanukovich has so far appeared reluctant to consider, a year before his term ends.
In Kiev, demonstrators on Independence Square held a vigil after dark for fallen comrades, lit by mobile phone screens held aloft.
Medics carried bodies on stretchers through lines of protesters who chanted "Heroes, heroes" to the dead.
Though armed militants on the barricades tend to be from the far-right fringe, the opposition has broad support. But many Ukrainians also fear violence slipping out of control:
"This is brother fighting brother," said Iryna, a local woman walking to Independence Square to donate syringes for blood transfusions. "We need to realise we're all one people."
Kiev residents emptied bank machines of cash and stockpiled groceries, with many staying off the streets.
In a sign of faltering support for Yanukovich, his hand-picked head of Kiev's city administration quit the ruling party in protest at bloodshed. (Additional reporting by Richard Balmforth, Alessandra Prentice, Vasily Fedosenko and Sabine Siebold in Kiev, John Irish in Paris and Francesco Guarascio and Adrian Croft in Brussels; Writing by Paul Taylor; editing by David Stamp)